please help e240 w211 misfire nightmare!!!!!!!!

[renopor]

hi all, i have a 2002 w211 e240 2.6, and its driving me up the wall, im hoping someone can point me in the right direction. it had random misfires showing up on a cylinders, ive changed all coils and leads, and plugs which solved this problem. but now it still has a p0300 misfire on cylinder no.4, but only when you drive it hard. i can clear the fault and the second i go above 4500rpm under load it throughs up an engine light and runs lump till i pull over and switch it off and on again. then it runs fine again. it will do the full rev range if you dont gun it and will happily drive around all day. ive changed the MAF and now the cats to no avail. ive changed around the injectors to see if the misfire would follow, but no its still at cylinder 4. any idea where i should go next?

 

[Barbanasos]

Have you measured the compression on that cylinder at any stage?

 

[lupi]

I agree with Barbanasos for a compression test.

You mentioned you already tried swopping with injectors, did you try
the same with coils and leads, and plugs, the fact they are
new doesn`t eliminate them from a possible fault.

 

[acidflame]

what about the intake?

 

[m1bnk]

I had a similar issue on my W210 E240. Having spent an arm and a leg on it I noted that when I'd changed the MAF it seemed better for a little bit. So, I unplugged and replugged the MAF a few times and it got better for a couple of weeks, then went back to normal.

Plug on the wiring harness showed some corrosion. A couple of hours vegging in front of the telly with dremel eventually cured the fault.

 

[adibchaiya]

I have W211 E240 with the same problem with renopor of misfiring. I had changed the ECU and it just goes fine for a few week and it doesn't solve the problem. My mechanic asked me to check the catalytic converter sensor if it is the cause to the problem. Is it relevant??